I‘ve always wanted to be a Machinist. For a while, I even subscribed to The Home Shop Machinist magazine, an uber-dorky niche mag aimed at the people who like to retreat to their basement machine shops to make things out of metal. There I learned to lust for a Bridgeport Mill, an Atlas Lathe, and a rotary table.

It’s probably for the best that I never bought any of those machines. Although the idea of being able to manufacture my own model internal combustion engines is an appealing one, getting into the machine-shop hobby is for folks with more available free time and money than I have right now.

But there is one machinist-like thing that I do from time to time, and that is to whip out the old tap and die set and cut some threads! If you have never threaded anything before, you should really try it soon, it is incredibly satisfying, and quite easy to do.

Most recently, I found myself wanting to install an oil temperature gauge in my car, which required that I create a place to install the sending unit.

It turns out that the oil filter fitting on my engine came with an un-used boss in the casting. This spot was used in some applications, not in others so I chose this spot to drill and tap a recepticle for the temp sensor.

Drill the hole

The first thing to do if you desire a threaded hole, is to drill a hole. The hole should be just under-sized, so that you don’t have to remove too much metal while cutting, but you want to have enough there to form the threads. Most taps will come with a spec telling you what size hole to drill

Cut some threads

The thread-cutting tap is essentially a tapered bolt, made from hard tool steel, which has multiple longitudinal flutes, that provide cutting edges. To cut your threads, all you have to do is thread the tool into the hole. Tap sets will come with a special T-handle that you use to turn the tool with by hand. I didn’t have one large enough for this particular tap, so I just turned it with a wrench. As the tap goes in, it cuts deeper and deeper until finally, youv’e got threads.

You need to use some oil to keep things going smoothly. I’ve found that light machine oil works well for steel, while WD-40 does a good job with aluminum.

Like I said, this is an immensely satisfying activity, you really should try it.

Next time, I’ll break out the dies, and make some bolts, just like grandpa used to make.

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7 Responses to “Thread cutting for beginners”

Geoffrey Says:

So, as a long time VW owner, I have long subscribed to the oil temperature is better or rather a useful adjunct to oil pressure readings.
So why does your gauge holder only have water temp/oil pressure and cylinder head temp. I would have taken oil temp over cylinder head temp in a water cooled vehicle any day.
Geoff

I applaud you for a project well executed, and would share only that I like to turn the tap BACK a bit every so often, to keep the new threads and tap cutters free of burr.

Mike Says:

Which VDO sensor did you go with here? Can’t make out the number I’m about to do the same to feed the oil temp gauge in my new gauge cluster. Great site btw, is serving as motivation do get my own MS-II project going. thanks, Mike

Thanks for the clear, correct advice in “Thread-cutting For Beginners”, which concentrated on tapping metal.

Unfortunately, you stopped before you broke out the dies.

I cannot find a source that explains the correct sizes of blank rod stock for using dies to make studs, etc.

I have tried to work it out from tap drill and tap size charts, which are easily found, but I can’t get it right.

Any advice?

Thanks, Larry

Jack Dinan Says:

In Thread-cutting for Beginners, you promised to break out the dies and show us how to chase a thread. I, like Larry Perkins, would like to see a table of blank rod diameters for this. Did you ever post the die article?